The multi-year research plan includes three separate studies that aim to investigate the developmental effects of child care quality for environmentally and biologically vulnerable children in order to inform the targeting of early care and education (ECE) policies and interventions designed to increase school readiness. The first study explores whether the federal child care subsidy program, which is the federal government's most comprehensive investment in ECE and the largest public early care program available to children from birth to age 3, goes beyond its primary goal of supporting parental employment to enhance the development of low- income children by shifting them onto trajectories of higher quality care. The second study considers the role of two more biologically-based risk factors - negative temperament and special needs status - in explaining the effect of exposure to high quality early care on cognitive and social-emotional development. The third study combines elements of the first two to explore whether the effects of higher quality early care on child outcomes among children who are environmentally vulnerable because they are poor vary depending on whether those children are also biologically vulnerable because they have negative temperaments or have been diagnosed with a special need. Data will be drawn from three datasets: to address the first and third questions, the newly available, nationally representative Early Childhood Longitudinal Study - Birth Cohort (ECLS-B) will be used. The ECLS-B collected extensive information from parents, child care providers, and kindergarten teachers along with direct assessments of children and observations of child care quality at multiple time-points. To address the second question, the Child Care and Temperament Over Time Study (CCTOTS) and data from the evaluation of Tulsa, Oklahoma's pre-k program (the Tulsa study) will be used. CCTOTS is a longitudinal study designed to assess the effect of child care experiences on the development of children classified as having negatively reactive and positively reactive temperaments in infancy, and as such contains highly reliable measures of temperament and child care quality. The Tulsa study is also unique in that it contains high-fidelity administrative data on children enrolled in high quality public pre-k and Head Start programs, as well as direct child assessment data and family background information from parent surveys. OLS regression, as well as econometric techniques aimed at reducing the threat of selection bias such as propensity score matching and regression discontinuity design will be used on the ECLS-B and Tulsa datasets. To capitalize on the repeated observations of children and child care settings in the CCTOTS data, OLS regression followed by latent growth curve analysis will be used. Findings from the proposed studies will inform efforts to support the school readiness of low-income children, children whose disadvantage stems from biologically-based sources, and children with the double disadvantage of both environmental and biological vulnerabilities.